Media channels, such as audio and video channels, have long been transmitted using application specific cables. For instance, two-core speaker cable is used to carry left and right audio channels from amplifiers to speakers.
More recently, media signals have been transmitted on computer based networks using protocols such as unicast or multicast. Unicast is a method of sending packets on a computer network to a single destination. The unicast packets must be retransmitted for every media device that wishes to receive the packets.
Multicast is typically used to refer to IP multicast, which is a protocol for efficiently sending to multiple receiver devices at the same time on TCP/IP networks by use of a multicast address. The computer network then operates to route the packets to each of the devices on the network that wish to receive the multicast packets.
Examples of computer based network designed to transport digital media is the computer network marketed by Telos. The Telos computer network operates using the multicast protocol and carries one channel of information per multicast stream of packets. All data transmitted on the computer network is homogenous. Each packet contains samples from a single channel, and all channels transmitted over the network use a 48 kHZ sampling rate and 20 bits of data per sample. By keeping the packet and sample formats homogeneous the Telos system always knows how to interpret an incoming packet. All it needs to know is which multicast address corresponds to each channel.
Another computer network marketed by CobraNet uses a unicast protocol. Transmitters are given repeating time intervals to transmit packets and the receiver is configured to receive the packets during that particular time interval.